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United States Patent |
5,028,355
|
Cope
,   et al.
|
July 2, 1991
|
Conductive polyurethane foam containing picric acid and analog thereof
Abstract
An electrically conductive polyurethane foam product is prepared by the in
situ combination of polyurethane-forming reactants and an effective amount
of a charge transfer agent selected from the group consisting of
tetracyanoethylene (TCNE), picric acid and analogs thereof, for lowering
electrical resistance of the foam product to less than 1.times.10.sup.12
ohms. In a preferred embodiment, the conductive foam product is
reticulated to a void volume of more than 80% after completion of the foam
forming reaction.
Inventors:
|
Cope; Richard P. (New City, NY);
Fisher; Leo (Fairlawn, NJ)
|
Assignee:
|
Crest-Foam Corporation (Moonachie, NJ)
|
Appl. No.:
|
367990 |
Filed:
|
June 19, 1989 |
Current U.S. Class: |
252/500; 252/511 |
Intern'l Class: |
H01B 001/00 |
Field of Search: |
521/118,125,128,130,164
252/500,511
|
References Cited
U.S. Patent Documents
3620986 | Nov., 1971 | Diehr et al. | 521/118.
|
3835102 | Sep., 1974 | Shinohara | 528/397.
|
4377646 | Mar., 1983 | Blount | 521/154.
|
4621106 | Nov., 1986 | Fracalossi et al. | 252/511.
|
4673720 | Jun., 1987 | Matsumura et al. | 252/500.
|
4703099 | Oct., 1987 | Regelman | 521/128.
|
Foreign Patent Documents |
18757 | Jan., 1982 | JP | 252/500.
|
24371 | May., 1982 | JP | 252/511.
|
115433 | Jul., 1982 | JP | 252/511.
|
185602 | Nov., 1982 | JP | 252/511.
|
135208 | Aug., 1984 | JP | 252/500.
|
Primary Examiner: Kight, III; John
Assistant Examiner: Daley; Dennis R.
Attorney, Agent or Firm: Darby & Darby
Parent Case Text
This application is a divisional application of U.S. patent application
Ser. No. 122,371, now U.S. Pat. No. 4,886,626, which is a
continuation-in-part of U.S. patent application Ser. No. 051,949, now
abandoned.
Claims
What is claimed is:
1. A three dimensional electrically conductive plastic foam structure
comprising a polyurethane foam containing an effective amount for lowering
the volume resistivity of said foam of a charge transfer agent selected
from the group consisting of picric acid and analogs thereof.
2. A three dimensional electrically conductive plastic foam structure
comprising a polyurethane foam containing an effective amount for lowering
the volume resistivity of said foam of picric acid.
3. A three dimensional electrically conductive structure according to claim
1, wherein said structure is prepared by reacting a polyol and an
isocyanate and comprises 0.02 to 2.5 parts per hundred parts by weight of
said polyol of said charge transfer agent.
4. A three dimensional electrically conductive structure according to claim
3 wherein said polyurethane foam comprises a reticulated polyurethane
foam.
5. A three dimensional electrically conductive structure according to claim
4, wherein the polyurethane foam comprises at least one graft polyol
reacted with an isocyanate in the presence of said charge transfer agent.
6. A three dimensional electrically conductive structure according to claim
5, wherein the charge transfer agent is dissolved in a suitable solvent
prior to reaction with said polyol and said isocyanate.
7. A three dimensional electrically conductive structure according to claim
4, wherein the polyurethane foam as formed from a graft polyol comprising
a copolymer of styrene and acrylonitrile grafted to an ethylene oxide
propylene oxide ether of glycerin.
8. A three dimensional electrically conductive structure according to claim
7, wherein the polyurethane foam is formed from 0.02 to 2.5 parts charge
transfer agent in a foam compatible organic solvent, 0 to 2.2 parts carbon
black, 1 to 8 parts water, in parts per hundred parts of said polyol.
9. A three dimensional electrically conductive structure according to claim
8, prepared from foam reactants containing at least one catalyst.
10. A three dimensional electrically conductive structure according to
claim 9 wherein the solvent is a member selected from the group consisting
of dipropylene glycol, chloroisopropyl phosphate and Tris-chloroethyl
phosphate, and containing from 2 to 10 percent of said solvent of charge
transfer agent.
11. A three dimensional electrically conductive structure according to
claim 4, wherein the polyurethane foam has a void volume greater than 80%.
12. A three dimensional electrically conductive structure according to
claim 4, wherein the polyurethane foam has a void volume greater than 90%.
13. A three dimensional electrically conductive structure according to
claim 12, wherein the effective amount of charge transfer agent is from
0.1 to 1.5 parts per hundred parts of polyol.
14. A three dimensional electrically conductive structure having a volume
resistivity of less than 10.sup.12 ohm cm, comprising
a polyurethane foam containing an effective amount for reducing the
electrical resistance of said foam to less than 10.sup.12 ohm cm of a
charge transfer agent selected from the group consisting of picric acid
and analogs thereof, incorporated into said foam in situ.
15. A three dimensional electrically conductive plastic foam structure
according to claim 14, wherein said charge transfer agent is in an amount
ranging from 0.02 to 2.5 php.
16. A three dimensional electrically conductive structure according to
claim 15, additionally comprising finely divided carbon black pigment
incorporated into said foam in situ.
17. A three dimensional electrically conductive plastic foam structure
according to claim 14, wherein said charge transfer agent is picric acid
in an amount ranging between 0.02 to 2.5 php.
18. A three dimensional electrically conductive structure according to
claim 14, wherein said polyurethane foam is thermally reticulated by
momentary exposure to an ignited combustible gas in a sealed chamber.
19. A three dimensional electrically conductive plastic foam structure
comprising a polyurethane foam containing an effective amount for lowering
the volume resistivity of said foam of a charge transfer agent selected
from the group consisting of
picric acid,
2,4-dinitrophenol,
2,5-dinitrophenol,
4-nitrophenol,
4-cyanophenol,
3-nitrophenol,
2,4,-dinitroanisol,
2-nitrophenol,
2-hydroxyacetophenone,
4-hydroxyacetophenone,
4-nitroanisol,
4-aminoacetopheone,
4-nitrobenzyl alcohol,
2-anitroaniline,
2,4-dihdroxyacetophenone,
4-nitrocatechol,
2-nitro-1-naphthol,
4-nitrobenzophenone,
4-nitrobenzaldehyde,
5-nitroanthranilonitrile,
2,6-dinitrocresol,
4-nitroaniline,
2,4-dinitroaniline,
2-nitroanisole,
4-nitrobenzonitrile,
4-nitroacetanilide, and
2,4-dinitro-1-naphthol sodium salt dihydrate.
20. A three dimensional electrically conductive plastic foam structure
according to claim 1 wherein said analogs are selected from the group
consisting of
2,4-dinitrophenol,
2,5-dinitrophenol,
4-nitrophenol,
4-cyanophenol,
3-nitrophenol,
2. 4-dinitroanisol,
2-nitrophenol,
2-hydroxyacetophenone,
4-hydroxyacetophenone,
4-nitroanisol,
4-aminoacetopheone,
4-nitrobenzyl alcohol,
2-nitroaniline,
2,4-dihdroxyacetophenone,
4-nitrocatechol,
2-nitro-1-naphthol,
4-nitrobenzophenone,
4-nitrobenzaldehyde,
5nitroanthranilonitrile,
2,6-dinitrocresol,
4-nitroaniline,
2,4-dinitroaniline,
2-nitroanisole,
4-nitrobenzonitrile,
4-nitroacetanilide, and
2,4-dinitro-1-naphthol sodium salt dihydrate.
21. A three dimensional electrically conductive plastic foam structure
according to claim 19, wherein said charge transfer agent present in an
amount of 0.2 to 2.5 php.
22. A thermosetting plastic foam composition having a volume resistivity of
10.sup.12 ohm cm or less comprising the product obtained by reacting a
polyol reactant selected from the group consisting of polyester polyols,
polyether polyols, mixtures of polyether and polyester polyols and
mixtures of polyether polyols and copolymer polyols with an isocyanate
reactant in the presence of a charge transfer agent selected from the
group consisting of picric acid and analogs thereof.
23. A foam composition according to claim 22, wherein said product is
reticulated and has a void volume of a least 80%.
24. The foam composition of claim 22 wherein said foam is non-reticulated
open cell foam.
25. The foam composition of claim 23 said polyol is a polyether polyol.
26. The foam composition of claim 23 said polyol is a mixture of a
polyether polyol and a copolymer polyol.
27. The foam composition of claim 23 wherein said foam has a void volume of
more than 90%.
28. The foam composition of claim 23, wherein said charge transfer agent is
picric acid.
29. A three dimensional electrically conductive plastic foam structure
comprising a polyurethane foam containing an effective amount for lowering
the volume resistivity of said foam of a charge transfer agent selected
from the group consisting of a compound of the formula
AR--X.sup.m --Y.sup.n,
where
AR is a radical selected from the group consisting of benzene, toluene and
naphthalene;
X is selected from the group consisting of OH, OCH.sub.3, CH.sub.2 OH,
NH.sub.2, NHCOCH.sub.3, CN, and O-M, where M is selected from the group
consisting of an alkalai metal salt of sodium and of potassium;
Y is selected from the group consisting of NO.sub.2 and COCH.sub.3 ;
m is an integer of 1 to 2; and
n is an integer from 1 to 3.
30. A three dimensional electrically conductive plastic foam structure
according to claim 27, wherein said charge transfer agent is present in an
amount of 0.2 to 2.5 php.
31. A method of preparing an electrically conductive polyurethane foam
composition which comprises:
reacting at least one polyester or polyether polyol with an isocyanate
compound in the presence of an effective amount for lowering the
electrical resistance of said polyurethane foam of a charge transfer agent
selected from the group consisting of picric acid and analogs thereof
under foam forming conditions.
32. A method according to claims 31 wherein said electrically conductive
polyurethane foam has an electrical resistance of less than 10.sup.12 ohm
cm.
33. A method according to claim 32, wherein said charge transfer agent is
present in an amount of 0.2 to 2.5 php.
34. A method according to claim 32, wherein said charge transfer agent is
present in an amount of 1.0 to 1.5 php.
35. A method according to claim 32, wherein said charge transfer agent is
picric acid.
36. A method according to claim 32, wherein said polyol comprises a graft
polyol.
37. A method of according to claim 32, which comprises adding finely
divided carbon black pigment to said foam reactants prior to or during
said reacting step.
38. A method according to claim 36, wherein the isocyanate compound
comprises toluene diisocyanate, the effective amount of charge transfer
agent ranges from between about 0.02 to about 2.5 parts per hundred parts
polyol dissolved in a polyurethane foam compatible solvent.
39. A method of preparing an electrically conductive polyurethane foam
composition having an electrical resistance of 10.sup.12 ohm cm or less
comprising the steps of:
reacting at least one graft polyol with toluene diisocyanate in the
presence of water, an amine catalyst, a tin catalyst, a cell control agent
and an effective amount for lowering the electrical resistance of said
foam of a charge transfer agent selected from the group consisting of
picric acid and analogs thereof in a suitable solvent under foam forming
conditions; and
reticulating said foam to a void volume of more than 80%.
Description
The present invention relates to three-dimensional expanded polyurethane
foam materials, such as flexible reticulated polyurethane foam
compositions, that are electrically conductive and have antistatic
properties. More specifically the invention relates to a polyurethane foam
having long-lasting and reliable electrical conductivity characteristics
and a volume resistivity of approximately 10.sup.12 ohm cm or less. This
foam is produced by combining conventional polyurethane foam-forming
reactants and an effective amount of a charge transfer agent such as the
electron acceptor compound tetracyanoethylene (TCNE), picric acid and
analogs thereof, under foam-forming conditions. In one preferred
embodiment, the conductive foam is subsequently reticulated by momentary
exposure to high temperature.
The analogs, according to the invention, have the formula AR--X.sup.m
--Y.sup.n, where AR is a radical selected from the group consisting of
benzene, toluene and naphthalene; X is selected from the group consisting
of OH, OCH.sub.3, CH.sub.2 OH, NH.sub.2, NHCOCH.sub.3, CN, and O-M, where
M is an alkalai metal salt of sodium or potassium; Y is selected from the
group consisting of NO.sub.2 and COCH.sub.3 ; m is 1 or 2; and n is from 1
to 3.
BACKGROUND OF THE INVENTION
Reticulated polyurethane foam products have been used for many years as
explosion suppression materials in the fuel tanks and containers of
gasoline and kerosene powered vehicles. The reticulated foam is a three
dimensional plastic material consisting of a plurality of strands which
are interconnected at spaced apart points to define void spaces or pores.
The product generally has a void volume of more than 80% and preferably
more than 90%. The reticulated foam material is installed inside the fuel
tank to occupy between about 50% and 100% of the interior dimensions of
the tank and serves to inhibit the rapid and uncontrolled spread of a
flame front when a spark is introduced into the fuel mixture. Thus,
polyurethane foams and foam linings are recognized as an important safety
feature in combustion technology, especially in the fuel tanks of military
and racing vehicles which are often operated under incendiary or static
electric discharge conditions. The reticulated urethane foam minimizes the
danger of fire or explosion resulting from exposure to static electric
discharges which often occur during operation or fueling, or as the result
of sparks that may be generated in crashes.
Within a fuel containment area provided with a reticulated polyurethane
foam, fuel is often subject to vibration and turbulent motion. The foam
tends to suppress fuel agitation due to vehicular motion, but static
charges can build up within the tank or containment area until they
overcome air resistance, and dangerous static electricity discharges can
occur, for example during a refueling operation. A static discharge, for
example between an ungrounded fuel hose nozzle and the metal frame of the
vehicle or tank, can damage sensitive electrical equipment, or worse, can
trigger an explosion within the tank. This problem is recognized in Martel
et al., Static Charge in Aircraft Fuel Tanks, Technical Report No.
AFWAL-TR-80-2049 (September, 1980). Therefore, there is a definite if not
urgent need for reliable and long-lasting means for safely controlling
static charges in the vicinity of combustion fuels and fuel gases,
especially during fueling operations.
The polyurethane foams conventionally used as fuel tank filler materials
are non-conductors having high electrical resistivity, e.g., a volume
resistivity of greater than 10.sup.13 ohm cm. Therefore, they cannot
dissipate or control static charges. Indeed, the high resistivity of
conventional foams may contribute to internal explosions caused by static
build-up and discharge, even while tending to suppress or contain
explosions.
Antistatic polyurethane foams which seek to achieve this purpose are known.
UnfortunatelY, the known compositions and methods suffer from degradation
and failure because they rely on antistatic agents that are not permanent;
they are too easily removed from the foam structure by washing or by
mechanical abrasion, or they degrade rapidly with normal aging and become
ineffective as antistatic materials.
One commercially available antistatic flexible foam is produced by
incorporating quaternary amines into the foam as an additive, by swelling
the finished foam, as described for example in Volz U.S. Pat. No.
4,578,406; or by using post foaming topical coatings such as conductive
carbon-containing surface coatings, described as prior art in the Volz
disclosure. Both of these known compositions and methods have certain
drawbacks, such as poor resistance to extraction by washing and lack of
resistance to mechanical abrasion. Moreover, these prior art foam
compositions require a post-foaming treatment in order to impart good
electrical conductivity to the foam, i.e. a relatively low electrical
resistivity on the order of 10.sup.12 ohm cm or less. Additionally, some
of the known antistatic foams can be very sensitive to humidity.
Fuji et al., U.S. Pat. No. 3,933,697 discloses an antistatic polyurethane
foam containing a quaternary ammonium salt as the antistatic agent.
Although the Fuji patent indicates that the quaternary additive can be
incorporated into the foam forming reactants, it has been found that foams
which depend upon quaternary salts for their electrical conductivity
properties do not retain such properties when the foam is exposed to
aqueous or solvent solutions for extended periods of time. Indeed, the
known quaternary salts are water soluble, and wash too readily from the
foam.
Berbeco U.S. Pat. No. 4,301,040 discloses a conductive polyurethane foam
incorporating finely divided conductive particles. However, it has been
found that the addition of an effective antistatic amount of finely
divided conductive particles results in severe deterioration of the
physical properties of the foam material. Foams of sufficiently low
resistivity to provide satisfactory electrical conductivity or antistatic
properties (less than 10.sup.12 ohm cm) are difficult to obtain using
known procedures and tend to lose their antistatic electrical properties
upon exposure to high humidity or solvents.
Other conductive compounds are known to be useful in combination with solid
polymers, including polyurethane resins, as opposed to polyurethane foams.
For example, British Patent No. 1,158,384; and (R. Knoesel et. al.) Bul.
Soc. Chim. Fr. 1969 (1) 294-301, disclose the use of ethenetetracarboxy
nitrile, also known as tetracyanoethylene (TCNE) to increase the
conductivity of special donor polymer resins such as
polydimethylaminostyrene and polyvinylphenothiazine.
German Offenlegungsschrift 28 38 720 discloses selectively conductive solid
epoxide or polyurethane casting resins containing TCNE. This reference
teaches that TCNE can effect the electrical conductivity of solid
synthetic resins as electron acceptors. Solid epoxy or polyurethane resins
can be combined with TCNE, and the TCNE polyurethane resin compositions
are shown to have an electrical conductivity of about
0.38.times.10-.sup.10 (ohm cm).sup.-1, which corresponds to a resistivity
of 2.6.times.10.sup.10 ohm cm.
These patents do not disclose or suggest that TCNE or picric acid can be
combined in situ with foam-forming ingredients as charge transfer agents,
to form a conductive polyurethane foam product, nor is there any
suggestion that such a foam product could retain its electrical
conductivity properties during the exothermic foam forming reaction (in
which reaction temperatures may reach 300.degree. F. or higher for several
hours) or the subsequent thermal reticulation treatment in which the
solidified foam mass is exposed to momentary plasma level temperatures
exceeding 2000.degree. C. and the internal temperature of the foam
material may reach 400.degree. F. or more.
While the use of conductivity enhancing electron acceptor compounds (charge
transfer agents) such as TCNE in solid polyurethane resins is known, the
permanent and in situ incorporation of TCNE or picric acid with
polyurethane foam reactants to form a permanent electrically conductive
polyurethane foam having a resistivity of less than about 10.sup.12 ohm cm
is not disclosed or suggested by the prior art.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electrically conductive
polyurethane foam that is suitable for use as a filler material in fuel
containers or tanks, particularly in vehicles having combustion powered
engines.
It is another object of the invention to provide a method for the in situ
preparation of an electrically conductive polyurethane foam.
It is yet another object of the invention to provide a stable, reliable and
long-lasting electrically conductive reticulated polyurethane foam
structure that retains its conductivity characteristics despite repeated
mechanical abrasion and exposure to heat, organic, and aqueous fluids.
A further object of the present invention is to provide an electrically
conductive reticulated polyurethane foam having void volume greater than
at least about 80%, and preferably more than 90%, using relatively small
quantities of the agent conferring electrical conductivity in the foam
forming reaction mixture.
Another object of the invention is an electrically conductive thermally
reticulated polyurethane foam prepared from a polyol and an isocyanate and
containing about 0.02 to 2.5 parts of TCNE per hundred parts by weight of
polyol (php) in the foam forming mixture.
Another object of the invention is an electrically conductive thermally
reticulated polyurethane foam prepared from a polyol and an isocyanate and
containing about 0.02 to 2.5 parts of picric acid per hundred parts by
weight of polyol (php) in the foam forming mixture.
It is another object of the invention to provide a polyurethane foam
composition having a non-degrading electrical volume resistance of less
than about 10.sup.12 ohm cm and preferably less than 10.sup.11 ohm cm.
These and other objects of the invention will be apparent to skilled
practitioners in the art from the following disclosure.
The objects of the invention are achieved by providing an electrically
conductive polyurethane foam, wherein the electrical resistivity of the
foam is desirably decreased to approximately 10.sup.12 ohm cm or less by
the integral incorporation of relatively small yet effective quantities of
a charge transfer agent selected from the group consisting of TCNE, picric
acid and analogs thereof, into the structure of the foam during foam
formation.
Advantageous polyurethane foam forming reactants include well-known
polyester and polyether polyols and diisocyanate compounds. Additional
reaction materials include water, catalyst compounds, and cell control
agents. According to the invention, the effective amount of charge
transfer agent (e.g., TCNE or picric acid) ranges from about 0.02 to 2.5
parts per hundred parts polyol (php), preferably 0.1 to 0.5 php.
Conductivity may be further enhanced by the incorporation of carbon black
pigment into the foam forming reaction mixture, when TCNE is the charge
transfer agent.
Surprisingly, the electrical conductivity properties afforded by in situ
incorporation of TCNE or picric acid survive the exotherm (on the order of
about 300.degree. F.) accompanying polyurethane foam formation, subsequent
reticulation of the foam under plasma temperature conditions (of about
2000.degree. C. or more), mechanical abrasion and long-term exposure to
aqueous and organic fluids. Accordingly, the foam products of the
invention are particularly well suited for use as an antistatic material,
for example as a filler in aircraft fuel tanks or as a packaging material
for delicate electronic components.
According to the invention, a conductive polyurethane foam is foamed in
situ, by known means, using conventional foam forming reactants comprising
one or more polyols, an isocyanate compound or composition, and an
effective amount of a charge transfer agent selected from the group
consisting of TCNE, picric acid and analogs thereof, for providing said
polyurethane foam with an electrical resistance of less than
1.times.10.sup.12 ohm cm in a suitable solvent. The optional presence of
finely divided carbon black pigment has been found to further enhance the
electrical conductivity of polyurethane foam made in accordance with the
present invention. The polyurethane foam materials of this invention
contain about 0.02 to 2.5 php of charge transfer agent (e.g., TCNE), 2.5
php being about the highest effective amount which can be incorporated
into the foam reactants without adversely affecting the physical
properties of the foam material unrelated to its electrical conductivity,
such as density and firmness. Preferably, the foam forming reactants
contain from 0.1 to 0.5 php of charge transfer agent, 0-2.2 php of carbon
and preferably 0.7-1.5 php of carbon may be optionally incorporated in the
foam. The optional carbon material is preferably added to the polyurethane
foam forming reactants in the form of a dispersion of finely divided
carbon in the polyol or a low viscosity resin e.g., propoxylated
ethoxylated glycerin or polydiethylene adipate.
According to the present invention a polyether or polyester urethane foam
is formed from isocyanate and hydroxyl containing (polyol) reactants by
known means, but with the charge transfer agent incorporated into the
reaction mixture prior to foam formation. The resulting polyurethane foam
may thereafter be reticulated to a void volume of greater than 80% and
preferably more than 90% if desired, preferably for example according to
the thermal reticulation method taught in Geen et al., U.S. Pat. No.
3,175,025 which is incorporated herein by reference. In preparing
electrically conductive polyurethane foams for use as fuel tank filler
materials, graft polyols are preferred as the polyol constituent of the
foam. One preferred graft copolymer is an ethylene oxide propylene oxide
ether of glycerin to which a copolymer of styrene and acrylonitrile has
been grafted. The invention is not limited, however, to use of these graft
materials as the polyol constituent. The flexible three dimensional
polyurethane foams of the invention may be prepared by reacting isocyanate
compounds with polyether polyols, polyester polyols, mixtures of polyether
and polyester polyols, or with mixtures of polyether polyols and copolymer
polyols such as for example the grafted polyether containing styrene and
acrylonitrile as described above, in the presence of the charge transfer
agent (TCNE, picric acid, etc.). The resulting electrically conductive
polyurethane foams exhibit a resistivity of less than 10.sup.12 ohm cm,
and retain this advantageously decreased electrical resistivity despite
exposure to exothermic foam forming conditions, relatively violent high
temperature reticulation procedures, immersion in water or fuel, and dry
heat aging.
The charge transfer agent that is incorporated into the foam in situ,
according to the invention, is at least one of TCNE, picric acid, and a
compound of the formula
AR--X.sup.m --Y.sup.n,
where
AR is a radical selected from the group consisting of benzene, toluene and
naphthalene;
X is selected from the group consisting of OH, OCH.sub.3, CH.sub.2 OH,
NH.sub.2, NHCOCH.sub.3, CN, and O-M, where M is an alkalai metal salt of
sodium or potassium;
Y is selected from the group consisting of NO.sub.2 and COCH.sub.3 ;
m is an integer of 1 or 2; and
n is an integer from 1 to 3.
BRIEF DESCRIPTION OF THE FIGURE
FIG. 1 is a graph showing the surface resistivity of TCNE foam as a
function of in situ TCNE concentration.
FIG. 2 is a graph showing the volume resistivity of TCNE foam as a function
of in situ TCNE concentration.
FIG. 3 is a graph showing the effect on electrical conductivity of adding
carbon back to TCNE polyurethane foams.
FIG. 4 is a graph showing the volume resistivity of picric acid foam as a
function of in situ picric acid concentration.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described with reference to a number of examples and
embodiments, and with reference to a number of comparative tests. It will
be understood by skilled practitioners that these examples, embodiments
and comparisons are illustrative only, and do not limit the scope of the
invention.
The polyurethane foams of the present invention may be prepared using the
one shot or the pre-polymer methods that are well known to the art and in
which hydroxyl containing ingredients (polyols) and polyisocyanates are
combined in the presence of well known catalysts, blowing agents, foam
stabilizers, flame retardants, pigments and extenders. Polyester based
polyurethanes, polyether based polyurethanes, copolymer polyol based
polyurethanes and mixtures of them may be used in making the conductive
foams of the invention, although polyether foams are preferred.
The polyisocyanate ingredients that are useful in the present invention
include, but are not limited to, toluene diisocyanate (TDI), which is
preferred, and polymers of diphenylmethane 4,4' diisocyanate (MDI).
Representative hydroxyl containing ingredients for use in the invention
include polyester and polyether polyols such as, for example, the
polypropylene glycol adipate glycerine ester and the ethylene oxide
propylene oxide ether of glycerin. Graft copolymers of hydroxyl containing
constituents which may also be employed as polyol constituents in
practicing the invention include ethylene oxide propylene oxide ether of
glycerin to which various amounts (between 20 and 40%) of a copolymer of
styrene and acrylonitrile have been grafted. The preferred graft polyol
for use in the present invention is a polymer consisting of the ethylene
oxide propylene oxide ether of glycerin to which 20% of a copolymer of
styrene and acrylonitrile has been grafted.
It has been surprisingly found that better electrical conductivity
properties are obtained using non-grafted polyols, when TCNE is the charge
transfer agent. Thus, the electrical conductivity of urethane foams made
using an ethylene oxide propylene oxide ether of glycerin as the hydroxy
containing constituent yields foams having an electrical resistivity of
2.times.10.sup.10 ohm cm, (e.g., using 0.2 php TCNE) while foams prepared
with a ethylene oxide propylene oxide ether of glycerin copolymerized with
40% of a styrene and acrylonitrile copolymer have an electrical resistance
of 3.times.10.sup.11 ohm cm.
According to the invention, polyether or polyester polyols are reacted in
situ under the usual polyurethane foam forming conditions with an
isocyanate and from 0.02 to 2.5 php (preferably 0.1 to 0.5 php) of a
charge transfer agent selected from the group consisting of TCNE, picric
acid and analogs thereof. The foam forming reaction is conducted in the
presence of the usual foam forming ingredients including catalyst
compounds (such as tertiary amines and organo tin compounds) cell control
agents and water to provide a polyurethane foam having an electrical
resistivity of about 10.sup.12 ohm cm or less. The electrically conductive
polyurethane foam product may be advantageously reticulated, so that the
foam product has a void volume of at least 80% and preferably more than
90%, with the thermal reticulation technique taught in Geen U.S. Pat. No.
3,750,025. In this procedure the three dimensional foam product is placed
in a sealed gas-filled chamber filled with a combustible gas and the gas
ignited to produce an explosion and a flame front in which the foam is
exposed to momentary plasma temperatures in excess of 2000.degree. C.
It has been found that polyurethane foams made with in situ charge transfer
agents are stable and retain their enhanced electrical conductivity
properties after exposure to elevated temperatures (284.degree. F. for 28
days) and long term immersion in aqueous and organic liquids at
temperatures up to 200.degree. C.
The invention will be illustrated in the following tables and working
examples. With reference to the tables, foam formulations are based on 100
parts by weight of polyol, as is customary. All other components are added
in parts by weight per hundred parts by weight of polyol (php), unless
otherwise noted. "E n" is a convenient shorthand notation for the
expression: "x 10.sup.n." Following is an identification of some of the
materials used in the working examples.
CEF is Tris chlorethyl phosphate (available from Stauffer Chemicals as
Fyrol CEF)
DPG is Dipropylene glycol
PCF is Tris chloroisopropyl phosphate available from Stauffer Chemical
Corp.
TDI 80/20 is an 80%/20% mixture of 2,4--diisocyanatomethylbenzene and
2,6--diisocyanatomethylbenzene commonly called toluene diisocyanate (or
80/20 TDI).
TDI 70/30 is a 70%/30% mixture of 2,4 diisocyanatomethylbenzene and
2,6--diisocyanatomethylbenzene commonly called toluene diisocyanate (or
70/30 TDI).
EXAMPLE 1
Manufacture of Electrically Conductive TCNE Foams
A wide variety of polyurethane foam compositions containing TCNE as the
charge transfer agent can be prepared, as illustrated below.
Formula 1
(A)
A polyurethane antistatic foam was prepared by admixing the following
ingredients on a conventional polyurethane foaming machine:
______________________________________
Material Parts
______________________________________
Pluracol 718 - a standard 3000 molecular weight
100
ethoxylated propoxylated glycerin polyol
manufactured by BASF.
Goldschmidt Silicone 8028 is a silicone surfactant
1.0
manufactured by Goldschmidt Corp., Hopewell, Virginia
Water 4.1
Union Carbide Amine Catalyst A-1
2.1
M & T Tin Catalyst T-125 - a dibutyl tin dialkyl
1.4
acid manufactured by M & T Chemicals, Inc.,
Rahway, New Jersey
Carbon Pigment - an 18% dispersion of carbon in
7.7
polyether polyol. (Dispersion 4824 manufactured
by Pigment Dispersions Inc., Edison, N.J.)
5% solution of TCNE in CEF 40.0
TDI 80/20 40.4
______________________________________
The resulting foam product was not reticulated after foam formation, but
had a surface resistivity of 3.1 E 9 ohms/square and a volume resistivity
of 2.2 E 9 ohm cm.
Formula 1
(B)
A graft antistatic foam was prepared using the following formulation.
______________________________________
Material Parts
______________________________________
Pluracol 994 is a graft polyol, (40%
100
acrylonitrile styrene copolymer) grafted on a
ethoxylated propoxylated glycerine (M W 5600)
manufactured by BASF.
Union Carbide Silicone L6202 is a silicone
1.2
surfactant manufactured by Union Carbide.
Water 4.6
Witco Tin Catalyst UL29 - is Diethyl tin mercaptide
0.3
manufactured by Witco Chemical Corp., Chicago, Ill.
Dabco 33LV - a 33% solution of triethylene diamine
0.4
in dipropylene glycol, manufactured by Air Products
& Chemicals, Inc., Allentown, Pennsylvania
5% solution of TCNE in PCF 4.0
TDI 80/20 51.0
______________________________________
The non-reticulated foam had a resistivity of 3.2 E 11 ohm cm.
Formula 1
(C)
A polyester antistatic foam was prepared using the following formulation:
______________________________________
Material Parts
______________________________________
F-76 Resin - a hydroxyl terminated ester resin -
100
specifically glycerin adipate polyoxyethylene,
manufactured by Witco Chemical Corp.
TDI 70/30 47.3
L536 - a silicone surfactant manufactured by Union
1.2
Carbide.
Water 3.7
N-Cocomorpholine 1.6
Amine Catalyst - Thancat M-75 a proprietary
1.2
tertiary amine, manufactured by Texaco Chemical Co.,
Bellaire, Texas
Amine Catalyst ADMA-6 - hexadecyl dimethyl amine,
0.5
manufactured by Ethyl Corp., Houston, Texas
5% solution of TCNE in PCF 6.0
______________________________________
This foam had a surface resistivity of 3.6 E 11 ohms/square and a volume
resistivity of 2.8 E 10 ohm cm. Moreover, when tested at 15% relative
humidity the foam had a static decay time (5000-50 volts) of 0.7 seconds
indicating that the foam rapidly dissipates a static electric charge.
Formula 1 (D)
A polyurethane antistatic foam was prepared using the following
formulation:
______________________________________
Material Parts
______________________________________
Niax 16-56 Polyol - a 3000 molecular weight
100
propoxylated ethoxylated glycerin polyol
manufactured by Union Carbide.
TDI 80/20 50.7
L6202 - a silicone surfactant manufactured by Union
1.2
Carbide.
T-120 - dibutyl tin mercaptide, manufactured by
0.5
M & T Chemical.
Water 4.1
Polycat 12 Amine Catalyst - a proprietary tertiary
0.8
amine manufactured by Air Products and Chemicals.
5% solution of TCNE in PCF 0.4
Carbon Pigment - a 18% dispersion of carbon in a
7.7
polyether polyol.
______________________________________
This foam had a volume resistivity of 4.7 E 11 ohm cm indicating the
effectiveness of in situ TCNE in conferring electrical conductivity
properties to polyurethane foam at low concentrations.
Formula 1 (E)
An antistatic 15ppi polyurethane foam was prepared using a graft polyol (as
the hydroxyl bearing constituent) on a commercial foaming machine using
the following formulation:
______________________________________
Material Parts
______________________________________
Pluracol 637 - a graft polyol 20% acrylonitrile
100
styrene copolymer grafted on a propoxylated
ethoxylated glycerin (M W 4200), manufactured by
BASF.
TDI 80/20 at 70.degree. F. 51.8
L6202 - a silicone surfactant manufactured by
1.0
Union Carbide.
Water 4.6
C-6N - a 33% solution of stannous octoate in
0.07
diisononyl phthalate, manufactured by Witco
Chemical Corp.
Amine Catalyst 33LV 0.59
5% solution of TCNE in PCF 6.0
Carbon Pigment - 18% dispersion of carbon in a
4.0
polyether polyol.
______________________________________
The polyol throughput of the foaming machine was 200 lbs/min and the mixing
head speed was 6000 RPM producing an antistatic graft foam bun 221/2" high
and 51" wide. The foam bun was cut into ten foot sections. One ten foot
long section of this foam bun was thermally reticulated suing the method
and apparatus described in Geen U.S. Pat. No. 3,175,025. After thermal
reticulation, the foam had a volume resistivity of 3.8 E 10 ohm cm, a
surface resistivity of 3.6 E 10 ohms/square and static decay (5000-500
volts) times at 15% relative humidity of 0.07 seconds and (5000-50 volts)
0.15 seconds demonstrating the excellent antistatic properties of the
foam.
Formula 1 (F)
A polyurethane foam was prepared by reacting the following ingredients in a
conventional polyurethane foaming process:
______________________________________
Material Parts
______________________________________
Poly G 32-52 a propoxylated ethoxylated glycerin
100
(M W 3300) manufactured by Olin Chemicals,
Stamford, Connecticut.
L-520 - a silicone surfactant manufactured by
1.0.
Union Carbide.
Water 3.5
Niax A-1 - dimethyl aminoethyl ether 70% in
0.4
dipropylene glycol manufactured by Union Carbide.
TBTO - tributyl tin oxide manufactured by M & T.
0.4
10% solution of TCNE in DPG 3.0
Lupranate M-10 - a polymeric diphenylmethane
73.3
diisocyanate, manufactured by BASF.
______________________________________
After the foam had cooled the volume resistance of the three dimensional
foam structure was measured. This foam had a volume resistance of
1.5.times.10.sup.10 ohm cm, displaying excellent antistatic properties.
Formula 1 (G)
A polyurethane foam was prepared by combining the following reactants:
______________________________________
Material Parts
______________________________________
Niax E-576 Polyol - an ethoxylated propoxylated
100
glycerin (M W 3700), available from Union Carbide.
L-564 - a silicone surfactant available from Union
1.0
Carbide.
Water 4.1
T-120 - dibutyl tin mercaptide, manufactured by
0.4
M & T Chemicals.
Niax A-4 - a tertiary amine mixture manufactured
1.3
by Union Carbide.
5% solution of TCNE in PCF 6.0
Isophorone diisocyanate 60.0
______________________________________
This non-reticulated foam had a volume resistivity of 8.2.times.10.sup.9
ohm cm.
EXAMPLE 2
Non-Reticulated TCNE Foams
A. Preparation
A series of TCNE non-reticulated polyurethane foams were prepared
incorporating 0.05, 0.1, 0.2, 0.3, 0.4, 0.6, 1.0 and 2.0 parts of TCNE.
The formulations shown in Table II were used in preparing these
non-reticulated TCNE foams. The appropriate quantity of TCNE was first
dissolved in Tris chloroisopropyl phosphate to make a 5% TCNE solution and
then combined with the other foam forming reactants just prior to foaming.
It was found that increasing amounts of TCNE caused increased conductivity
(i.e. decreased electrical resistance) as shown in FIGS. 1 and 2.
TABLE I
______________________________________
FOAM FORMULATIONS
Material Parts
______________________________________
994 50
16-56 50
L6202 1.2
Water 4.6
33LV 0.4
UL29 0.3
TDI (80/20) 51.0
TCNE (0.05), (0.1), (0.2), (0.3),
(0.4), (0.6), (1.0), and (2.0)
______________________________________
The surface and volume resistivities of the TCNE containing polyurethane
foams made pursuant to Table I were determined and the TCNE concentration
was graphed against the respective electrical resistance values, as in
FIGS. 1 and 2.
B. Resistivity
After completion of the foaming reaction and cooling of the product to
ambient temperatures the volume resistivity of the resulting
non-reticulated foam product was measured using the following equipment
and procedures (which are essentially those of ASTM-D-257-78). A circular
guard ring electrode having a center electrode ring (53 mm in diameter)
and an outer electrode ring (101 mm in diameter) is placed in contact with
a foam specimen. A base electrode (or flat steel plate) is placed on the
opposite side of the foam specimen. The inner (+) electrode and the base
(-) electrode are connected to a "Dr. Kamphausen Milli To" ohmmeter
(Monroe Electronics, Londonville, N.Y.) to produce a vertical field
through the foam specimen between the plates. The guard electrode is
connected to the ground. A TCNE foam specimen (approximately
5".times.5".times.1" thick) is placed between the electrodes, the Milli To
voltage set to 500 volts and the variable resistance adjusted until a
resistance reading is obtained on the meter. After allowing the meter to
stabilize for about 1 minute, the resistance of the specimen, the
temperature / humidity and the thickness of the specimen are recorded. The
volume resistivity is calculated using the following formula
##EQU1##
The surface resistance of a foam specimen is measured using the same
apparatus, but with the inner electrode being the anode (+) of the outer
electrode being the cathode (-) and the base plate serving as ground. The
surface resistivity is the measured resistance .times.10. These tests are
conducted according to ASTM D257, a standard for surface resistivity
measurement.
There are at least three standards for antistatic compounds. Electronics
industry standard IS-5 requires a static decay rate of a 99% charge decay
in less than two seconds and a surface resistivity of less than
1.times.10.sup.13 ohms. Military standard MIL-B-81705B is a military
specification for packaging materials for electrosensitive devices and
explosives. It specifies that the charge induced by the application of
5000 volts at less than 15% relative humidity must decay completely within
2 seconds. This standard does not have any surface resistivity
requirement. The National Fire Protection Association standard
NFPA-56A-1978 for operating room products requires that an applied charge
drop to 10% of its initial value within 0.5 seconds, at a relative
humidity of 50%.
Static decay is measured according to Federal Test Method Standard 101B
Method 4046. A 5000 volt charge is applied to the surface of the specimen,
the maximum charge accepted is measured, and the time required to
dissipate the charge after a ground is applied is determined.
These procedures and apparatus were used for the measurements reported in
the Examples.
In this present example, TCNE was found to be a particularly effective
antistatic agent for graft foam (i.e. foam produced used graft polyols).
Use of a grafted polyol (e.g. Pluracol 994) and 0.2 php TCNE produced
urethane foam with a volume resistivity of 8.55.times.10.sup.10 ohm cm.
EXAMPLE 3
Resistance to Extraction and Aging of Non-reticulated TCNE Foam Materials
The permanence of the antistatic properties of the TCNE polyurethane foam
produced in Example 2 was measured by extraction with hot water,
extraction in JP-5 (petroleum jet fuel) and also by dry heat aging at
300.degree. F., as shown in Table II. The JP-5 extraction test was
conducted by continuously squeezing a 5".times.5".times.1" sample of the
antistatic foam in JP-5 jet fuel for 5 minutes, wringing out the jet fuel,
washing 1 minute in cold water, and drying at 158.degree. F. The foam Was
then conditioned at room temperature at 50% relative humidity for 16 hours
and the surface and volume resistivities was determined according to ASTM
D 257. The procedure for testing in hot water was to immerse a foam sample
5".times.5".times.1" thick in 140.degree. F. water squeezing for 5
minutes, remove the foam, wring out the water, allow the foam to dry at
158.degree. F., condition at 50% relative humidity for 16 hours and then
make surface and volume resistance measurements. Hot air aging was
conducted in a hot air oven. After removal from the oven and cooling to
ambient temperature the foam was conditioned at 50% humidity for 16 hours
and the volume and surface resistivity was determined. The test results
are reported in Table II, which indicates that the electrical conductivity
conferred on the foam by foaming in situ with TCNE is essentially
unaffected in foam material exposed to hot water and JP-5 jet fuel and
that the antistatic properties resist dry heat aging.
TABLE II
______________________________________
TCNE Before After
(php) Treatment Conditions
Treatment Treatment
______________________________________
0.4 Foam sample 5" .times. 5" .times. 1" thick.
Squeezed 5 min. in 140.degree. F. water
Surface Resistivity (ohms/sq.)
4.40 E 10 9.80 E 10
Volume Resistivity (ohm cm)
2.67 E 10 2.16 E 10
0.4 Squeezed 5 min. JP-5
Surface Resistivity (ohms/sq.)
5.26 E 10 1.90 E 10
Volume Resistivity (ohm cm)
4.02 E 10 9.91 E 9
Dry heat aging at 300.degree. F.
0.1 1. 1 hour
Surface Resistivity (ohms/sq.)
1.46 E 12 2.45 E 12
Volume Resistivity (ohm cm)
3.11 E 11 5.77 E 11
0.2 2. 2 hours
Surface Resistivity (ohms/sq.)
1.98 E 11 8.97 E 10
Volume Resistivity (ohm cm)
8.55 E 10 7.66 E 10
0.2 3. 3 hours
Surface Resistivity (ohms/sq.)
1.98 E 11 1.22 E 11
Volume Resistivity (ohm cm)
8.55 E 10 1.05 E 11
______________________________________
EXAMPLE 4
- Resistance to Extraction and Aging in Reticulated TCNE / Polyurethane
Foam Samples
The foam products prepared in Example 2 but containing 0.1, 0.2, 0.3 and
0.4 php TCNE were thermally reticulated using the process of Geen U.S.
Pat. No. 3,175,025 and thereafter samples were subjected to impregnation
with hot water, autoclaving and dry heat aging. Thereafter the surface and
volume resistivity of the foam samples (5".times.5".times.1"), each -
containing different amounts of TCNE, was tested.
The electrical conductivity of TCNE reticulated foam is not meaningfully
affected by immersion in hot water, steam or by long exposure to dry heat.
TCNE is permanently incorporated into the foam. As shown in Table III,
under the severe conditions of one week autoclaved aging, volume
resistivity remained substantially constant in a foam containing 0.4 php
TCNE.
TABLE III
______________________________________
TCNE Before After
(php) Treatment Conditions
Treatment Treatment
______________________________________
0.3 a. Squeezed 5 min. in
140.degree. F. water
Surface Resistivity (ohms/sq)
1.03 E 11 2.10 E 11
Volume Resistivity (ohms cm)
5.05 E 10 1.41 E 11
0.4 b. Autoclaved 250.degree. F.
1. 5 hours
Surface Resistivity (ohms/sq)
5.95 E 10 1.07 E 11
Volume Resistivity (ohm cm)
3.95 E 10 4.08 E 10
0.4 2. 24 hours
Surface Resistivity (ohms/sq)
5.15 E 10 4.10 E 10
Volume Resistivity (ohm cm)
3.06 E 10 2.99 E 10
0.4 3. 48 hours
Surface Resistivity (ohms/sq)
5.15 E 10 2.62 E 10
Volume Resistivity (ohm cm)
3.06 E 10 2.99 E 10
0.4 4. 72 hours
Surface Resistivity (ohms/sq)
5.15 E 10 2.82 E 10
Volume Resistivity (ohm cm)
3.06 E 10 2.18 E 10
0.4 5. 96 hours
Surface Resistivity (ohms/sq)
5.15 E 10 3.32 E 10
Volume Resistivity (ohm cm)
3.06 E 10 1.85 E 10
0.4 6. 168 hours
Surface Resistivity (ohms/sq)
5.15 E 10 1.84 E 10
Volume Resistivity (ohm cm)
3.06 E 10 1.19 E 10
0.2 c. Dry Heat Aging at 284.degree. F.
1. 24 hours
Surface Resistivity (ohms/sq)
1.59 E 11 1.74 E 11
Volume Resistivity (ohm cm)
7.89 E 11 1.03 E 11
0.2 2. 48 hours
Surface Resistivity (ohms/sq)
1.59 E 11 2.72 E 11
Volume Resistivity (ohm cm)
7.89 E 11 1.58 E 11
0.2 3. 72 hours
Surface Resistivity (ohms/sq)
1.59 E 11 3.85 E 11
Volume Resistivity (ohm cm)
7.89 E 11 1.73 E 11
0.2 4. 96 hours
Surface Resistivity (ohms/sq)
1.59 E 11 5.83 E 11
Volume Resistivity (ohm cm)
7.89 E 11 1.29 E 11
0.2 5. 168 hours
Surface Resistivity (ohms/sq)
1.58 E 11 4.26 E 11
Volume Resistivity (ohm cm)
7.89 E 11 3.18 E 11
______________________________________
EXAMPLE 5
In Situ Reticulated TCNE Foams
Reticulated foams were prepared containing 0.1, 0.2, 0.3 and 0.4 parts
TCNE. Except for TCNE which ranged from 0.1 to 0.4 php (as described
above) the same formulations were used in these reticulated foams as were
employed in making the non-reticulated foams of Example 2. The physical
properties of these foam samples are shown in Table IV.
TABLE IV
______________________________________
Parts TCNE
0.1 0.2 0.3 0.4
______________________________________
A. Before Reticulation
Air Flow (cfm)
0.5 1.0 6.0 7.0
Density (pcf)
1.23 (top)
1.38 (top)
1.48 1.36 (top)
25% CLD (1) 0.52 0.51 0.57 0.54
Surface Resistivity
6.75 E 11
2.44 E 11
8.35 E 10
4.63 E 10
Volume Resistivity
2.52 E 11
9.36 E 10
4.90 E 10
3.68 E 10
B. After Reticulation
Air Flow (cfm)
8.0 8.3 8.2 9.6
Density (pcf)
1.50 1.42 1.86 1.97
25% CLD 0.42 0.48 0.67 0.67
Surface Resistivity
4.86 E 11
1.67 E 11
6.91 E 10
4.43 E 10
Volume Resistivity
1.60 E 11
6.46 E 10
5.22 E 10
3.92 E 10
Tensile Strength (psi)
21.1 22.0 24.1 21.5
Elongation 260 270 210 200
Tear Strength (psi)
4.4 -- -- 4.7
______________________________________
(1) Compression load deflection
Reticulation is not detrimental to the excellent conductive and antistatic
properties imparted to polyurethane foam structures containing small
quantities of TCNE, as shown by the substantially unchanged resistivity
characteristics of the foam specimens before and after reticulation. Also,
the TCNE did not adversely affect the strength of the foam.
While not being bound by any specific theory of operation for the invention
it is believed that the resistance to extraction of TCNE, which accepts
electrons from nitrogen-containing polymers in the foam, is due to
formation of a chemical bond between the skeletal structure of the
polyurethane and the TCNE during the in situ foam-forming operation.
EXAMPLE 6
Humidity Exposure Test
The electrical (volume) resistance of TCNE containing polyurethane foams
made as in Example 2 was measured at various relative humidities from 7 to
99%.
Volume resistance measurements showed that polyurethane foam made with TCNE
is not particularly sensitive to humidity changes. This is illustrated in
the results of the humidity exposure test reflected in Table V below. Each
foam specimen was exposed to room humidity of 7%, 50% and 99% for 16
hours. The foams tested below were samples (5".times.5".times.1") of the
same foams used in Example 5 above.
TABLE V
______________________________________
TCNE in Foam (php)
0.1 0.2 0.3 0.4
______________________________________
Surface Resistivity
(ohms/sq.)
7% R.H. 7.38 E 11
2.07 E 11
7.98 E 10
5.85 E 10
50% R.H. 3.27 E 11
1.40 E 11
7.00 E 10
4.34 E 10
99% R.H. 1.12 E 11
6.17 E 10
3.59 E 10
2.94 E 10
Volume Resistivity
(ohm cm)
7% R.H. 2.04 E 11
8.23 E 10
6.30 E 10
4.51 E 10
50% R.H. 9.07 E 10
4.46 E 10
3.93 E 10
2.43 E 10
99% R.H. 2.34 E 10
1.41 E 10
1.29 E 10
8.07 E 9
______________________________________
EXAMPLE 7
Carbon Black Plus TCNE
The in situ incorporation of carbon black pigment into the foam further
decreases its electrical resistance (and increases electrical
conductivity), but only if TCNE is also present. This was confirmed by
incorporating finely divided carbon black into polyurethane foam
containing TCNE and prepared from the same constituents as in Example 2
but containing 0.1, 0.2, 0.3, 0.4 and 0.5 parts TCNE. FIG. 3 illustrates
the enhanced conductivity of foam containing TCNE and carbon black. One
suitable method for incorporating carbon in the foam reactants is to use
an 18% dispersion of carbon in a polyether polyol (available from PDI as
Dispersion No. 4824).
The conductivity enhancement realized by incorporation of carbon black
pigment with TCNE was surprising since the incorporation of carbon pigment
in reticulated 15ppi polyurethane foam (80/20 TDI+Pluracol 637) does not
appear to lower its resistance value. Several TCNE foams were prepared
containing carbon black to confirm the synergistic effect of carbon black
and TCNE in decreasing electrical resistance. The volume resistivity of
these foams at different concentrations of TCNE was compared with that of
non-pigmented TCNE foams. As shown in FIG. 3, the incorporation of carbon
black pigment and TCNE in polyurethane foam forming ingredients does
indeed lower the electrical resistance of the resulting polyurethane foam
material beyond the decrease that is attainable with incorporation of TCNE
alone.
TCNE is a solid agent, and its dispersion in a polyol yields a foam product
with holes in the foam. Unless it is dissolved in a suitable solvent prior
to admixture with the other foam forming reactants, combination of TCNE
with such materials will not produce an acceptable electrically conductive
three dimensional polyurethane foam product. Therefore, the TCNE must be
dissolved in a suitable aqueous or organic solvent prior to combination
with the other foam forming reactants. Water or any of a number of diverse
organic solvents may be used to dissolve the TCNE, provided they are
compatible with the foam material and do not hinder the foam forming
process. Solutions containing between 1 and 10% TCNE and preferably 5-10%
TCNE yield acceptable foam products and facilitate combination of TCNE and
the other foam forming ingredients. Among the useful organic solvents for
TCNE are Dipropylene glycol, Tris chloroisopropyl phosphate, Tris
chloroethyl phosphate and TDI. Solutions of TCNE in PCF and CEF caused no
detrimental effect on the electrical conductivity of the resulting foam
product. Therefore, PCF and CEF are an especially preferred as TCNE
solvents.
EXAMPLE 8
Two reticulated foam products were made pursuant to Example 2 but
substituted respectively with Pluracol 994 (graft copolymer) and Pluracol
637 polyol graft copolymer formulation. The volume resistivity of each
sample was measured and is shown in Table VI.
TABLE VI
______________________________________
Volume Resistivities of TCNE Foams Prepared
With Different Polyol Systems
Parts TCNE
Polyol 0.1 0.2 0.3
______________________________________
100% Pluracol 637
9.50 E 10 3.87 E 10
2.14 E 10
50% Pluracol 1.25 E 11 3.34 E 10
2.58 E 10
994:50% 16-56
______________________________________
It can be seen from the data in Table VI that the volume resistivities of
TCNE foams prepared with the two polyol systems are approximately
equivalent within the preferred TCNE ranges of the invention. Both 100%
Pluracol graft copolymer 637 polyol and a 50:50 blend of Pluracol 994 and
Niax 16-56 polyol can advantageously be used for the production of TCNE
containing antistatic polyurethane foam.
EXAMPLE 9
Abrasion Resistance of Reticulated TCNE Foams
The resistance of a reticulated foam to mechanical abrasion was estimated
by rubbing a 5".times.5".times.1" thick sample of a finished foam product
on a medium emery paper twenty times. The foam product was made from the
following reactants:
TABLE VII
______________________________________
Formulation A
Formulation B
Formulation C
Parts Parts Parts
______________________________________
Pluracol 637
100 100 100
5% TCNE 2.0 4.0 6.0
in PCF
PDI 4824 7.7 7.7 7.7
L6202 1.0 1.0 1.0
H.sub.2 O
4.6 4.6 4.6
33LV 0.4 0.4 0.5
UL29 0.3 0.3 0.5
TDI 51 51 51
______________________________________
The results reported in Table VII (A) indicate that the electrical
conductivity property of the TCNE foam is not eliminated or substantially
diminished by mechanical abrasion.
TABLE VII(A)
______________________________________
Before Abrasion
After Abrasion
______________________________________
Formulation A
0.1 Parts TCNE
Surface Resistivity (ohms/sq)
2.14 E 11 1.97 E 11
Volume Resistivity (ohm cm)
7.41 E 10 6.83 E 10
Formulation B
0.2 Parts TCNE
Surface Resistivity (ohms/sq)
5.12 E 10 5.18 E 10
Volume Resistivity (ohm cm)
3.14 E 10 2.94 E 10
Formulation C
0.3 Parts TCNE
Surface Resistivity (ohms/sq)
3.49 E 10 5.31 E 10
Volume Resistivity (ohm cm)
2.65 E 10 2.67 E 10
______________________________________
EXAMPLE 10
Temperature Resistance
The sensitivity of the electrical resistance values of TCNE foams to
temperature was measured on several non-reticulated TCNE containing foam
specimens made pursuant to Table VIII (A).
TABLE VIII(A)
______________________________________
Parts
______________________________________
Niax 16-56 100
L6202 1.2
H.sub.2 O 4.6
UL29 .4
33LV .3
5% Solution of TCNE (0.02) (0.05)
in PCF (0.1) (0.2) (0.3)
TDI 53.2
______________________________________
Tests were performed at 40.degree. F., 70.degree. F., 158.degree. F., and
300.degree. F. The reticulated foam formulations contained TCNE ranging
from 0.02 to 0.3 php. It was discovered that the conductivity of the TCNE
foam is only slight better as the temperature of the foam is increased.
For example, at 0.02 parts TCNE, volume resistivity decreased from
3.52.times.10.sup.11 at 40.degree. F. to 1.00.times.10.sup.11 at
300.degree. F.
Table VIII (B) illustrates the slight decrease in volume resistivity with
increased temperature of conventional (non-graft) polyurethane foams.
TABLE VIII (B)
______________________________________
The Effect of Temperature on Resistivity of TCNE Foam
Volume Resistivity (ohm cm)
0.02 parts 0.05 parts
0.1 parts
0.2 parts
0.3 parts
TCNE TCNE TCNE TCNE TCNE
php php php php php
______________________________________
40.degree. F.
3.52 E 11
1.52 E 11 4.77 E 10
3.60 E 10
1.76 E 10
70.degree. F.
3.05 E 11
1.01 E 11 3.71 E 10
2.26 E 10
1.62 E 10
158.degree. F.
2.94 E 11
7.95 E 10 3.51 E 10
1.66 E 10
1.44 E 10
300.degree. F.
1.00 E 11
4.03 E 10 2.79 E 10
1.37 E 10
1.36 E 10
______________________________________
A particularly preferred formulation for the TCNE reticulated foam of the
present invention is:
______________________________________
Preferred
Material Parts
______________________________________
Pluracol 637 100
TCNE 0.2
Fyrol PCF 3.8
L6202 1.0
PDI black #4824 7.7
Water 4.6
33LV 0.4
UL29 0.3
TDI (80/20) 51.0
______________________________________
Water level of the foam material can be adjusted to give the density
required, and can be varied between 1.4 php for a 6 pcf (pounds per cubic
foot) foam to 5.0 php for a 1.4 pcf foam. Generally, the lower the water
content of a foam material the lower the electrical resistance of the
foam.
EXAMPLE 11
Electrically Conductive Picric Acid Foams
A wide variety of polyurethane foam compositions containing picric acid and
analogs thereof as the charge transfer agent can be prepared, as
illustrate below.
Formula 11
(PICRIC ACID)
A polyurethane antistatic foam was prepared by admixing the following
ingredients on a conventional polyurethane foaming machine:
______________________________________
Material Parts
______________________________________
Poly G 32-52 a propoxylated ethoxylated glycerin
100
(M W 3300) manufactured by Olin Chemicals,
Stamford, Connecticut.
Picric Acid 1.0
Fyrol PCF 5.0
Water 3.6
Union Carbide Silicone L6202 is a silicone
1.0
surfactant manufactured by Union Carbide.
Witco Tin Catalyst UL29 - is Diethyl tin mercaptide
1.5
manufactured by Witco Chemical Corp., Chicago, Ill.
Dabco 33LV - a 33% solution of triethylene diamine
1.2
in dipropylene glycol, manufactured by Air Products
& Chemicals, Inc., Allentown, Pennsylvania
TDI 80/20 43.7
______________________________________
The resulting foam product had a rise time of 120 seconds, a density of
1.87 pcf, an airflow of 0.90 cfm, and a surface resistivity of 2.9 E 10
ohm/sq. This formula can be varied by replacing picric acid with
electrically conductive analogs, such as those in Formulas 11(A-J), as
shown below.
TABLE IX
______________________________________
BASIC FOAM FORMULATION (php)
______________________________________
32-52 100
FYROL PCF 5.0
WATER 3.6
L6202 1.0
UL29 1.0
33LV 1.0
TDI (80/20) 43.7
CHARGE TRANSFER AGENT 1.0
______________________________________
The following data was obtained for each tested picric acid analog. (Note
that FYROL PCF was omitted in Formulas H and J).
__________________________________________________________________________
SURFACE RESISTIVITY FOR PICRIC ACID ANALOGS
RESISTIVITY
RISE
DENSITY
AIRFLOW
FORMULA
CHARGE TRANSFER AGENT
OHMS/SQ.
TIME
PCF CFM
__________________________________________________________________________
A 2,4-DINITROPHENOL
4.3 E 10
90 s
1.79 3.3
B 2,5-DINITROPHENOL
9.1 E 10
49 s
1.72 1.79
C 4-NITROPHENOL 1.0 E 11
37 s
1.68 0.12
D 4-CYANOPHENOL 1.4 E 11
34 s
1.70 0.14
E 3-NITROPHENOL 2.0 E 11
28 s
1.66 0.08
F 2,4-DINITROANISOL
2.4 E 11
36 s
1.62 0.15
G 2-NITROPHENOL 4.3 E 11
30 s
1.64 0.31
H 2-HYDROXYACETOPHENONE
4.8 E 11
26 s
1.58 0.18
I 4-HYDROXYACETOPHENONE
5.4 E 11
31 s
1.65 0.15
J METHYL SALICYLATE
1.4 E 12
30 s
1.63 0.09
CONTROL
NONE 2.4 E 12
30 s
1.58 0.14
__________________________________________________________________________
All of these exemplary picric acid analogs exhibit effective antistatic
properties, except methyl salicylate. Typical surface resistivity values
for picric acid and its analogs is about 5.6 E 10 ohm/sq. for 0.5 php, and
2.4 E 12 for 1.0 php of charge transfer agent. When no picric acid analog
is used, the resistivity is about 2.9 E 10.
Although most of the formulations in the above examples use PCF as a
solvent for picric acid, or an antistatic analog thereof, other solvents
can also be used. For example, generally equivalent results are obtained
using 16.7% picric acid in Fyrol CEF or Dipropylene glycol, or 25% picric
acid in Thermolin 101 or Antiblaze 100.
EXAMPLE 12
Additional Antistatic Picric Acid Formulations
A number of additional foam formulations and picric acid analogs have been
tested, and exhibit antistatic properties.
Formula 12 (A)
A polyurethane foam was prepared by admixing the following ingredients on a
conventional polyurethane foaming machine:
______________________________________
Material Parts
______________________________________
Pluracol 718 - a standard 3000 molecular weight
100
ethoxylated propoxylated glycerin polyol
manufactured by BASF.
Silicone L520 is a silicone surfactant
1.0
manufactured by Union Carbide Corp.
Water 4.1
T-120 Dibutyl tin mercaptide, manufactured
1.2
by M&T Chemicals, Inc., Rahway, N.J.
Niax A-4, a tertiary amine mixture made by
1.2
Union Carbide Corp.
16% solution of picric acid in Fyrol
6.0
PCF-tri(chloropropyl) Phosphate, made by
Stauffer Chemical Co., Westport, CT.
TDI 80/20 49.3
______________________________________
The resulting foam product has a surface resistivity of 1.6 E 9
ohms/square.
Formula 12 (B)
A polyurethane antistatic foam was prepared by admixing the following
ingredients in a conventional polyurethane foaming process:
______________________________________
Material Parts
______________________________________
Poly G 32-52, A propoxylated ethoxylated
100
glycerin (MW 3300) made by Olin Chemicals
Silicone L6202, a silicone surfactant
1.0
manufactured by Union Carbide Corp.
Water 4.3
T-125 Dibutyl tin dialkyl acid, made
1.0
by M&T Chemicals, Inc., Rahway, N.J.
Niax A-1, Dimethyl aminoethyl ether 10% in
1.0
dipropylene glycol, made by Union Carbide
16.7% solution of picric acid in Fyrol PCF
3.0
Lupranate M-10, a polymeric diphenylmethane
73.3
diisocyanate made by BASF.
______________________________________
After cooling, the resulting three-dimensional foam product has a surface
resistivity of 1.65 E 11 ohms/square, demonstrating excellent antistatic
properties.
Formula 12 (C)
A polyurethane antistatic ester foam was prepared by admixing the following
ingredients in a conventional polyurethane foaming process:
______________________________________
Material 1 2 3
______________________________________
Fomrez 76, a hydroxyl termi-
100 100 100
nated ester specifically glycerine
adipate polyoxyethylene, made
by Witco Chemical.
N-cocomorpholine 1.5 1.5 1.5
Thancat M-75, a tertiary amine
1.8 1.8 1.8
blend made by Texaco Chemical
Co.
Water 4.0 4.0 4.0
L-536, a silicon surfactant made
0.7 0.7 0.7
by Union Carbide Corp.
Fomrez M66-82A, a mixture of
0.6 0.6 0.6
surfactants made by Witco
Fomrez YA 49-49, an organic
0 4.0 4.0
hydroxyl terminated ester cross-
linker, made Witco Chemical.
16% solution of picric acid in
3.0 6.0 9.0
Fyrol PCF
TDI 80/20 52.7 52.7 52.7
SURFACE RESISTIVITY
2.5 E 11 1.4 E 11 1.0 E 11
(OHM/SQ.)
VOLUME RESISTIVITY
1.0 E 11 6.0 E 10 3.5 E 10
(OHM CM)
______________________________________
These examples illustrate the excellent antistatic properties of ester
foams containing picric acid.
Formula 12
(D)
A series of antistatic ether foams were prepared as follows, with amounts
given as parts per hundred polyol (php).
______________________________________
MATERIAL 1 2 3 4 5 6
______________________________________
Niax 16-56
100 100 100 100 100 100
L6202 1.1 1.1 1.0 1.0 0.9 0.9
Water 4.7 4.7 4.1 4.1 3.4 3.4
Fomrez 0.8 1.2 0.8 1.5 0.8 1.2
UL29
Dabco 33LV
0.8 1.2 0.8 1.2 0.8 1.2
16% Picric
3.0 6.0 3.0 6.0 3.0 6.0
Acid/PCF
Methylene
5.0 5.0 0 0 0 0
chloride
TDI (80/20)
60.6 60.6 49.3 49.3 47.0 47.0
DENSITY 1.25 1.25 1.62 1.65 1.82 1.83
(PCF)
SURFACE 7.4E11 7.4E10 6.0E10
3.2E10
5.6E10
2.8E10
RESISTI-
VITY
STATIC 1.0 0.3 0.3 0.1 0.4 0.2
DECAY
______________________________________
Niax 1656 is a 3000 molecular weight polyol, manufactured by Union Carbid
Corp. The surface resistivity is measured as ohm/square. The static decay
was measured at 5000-50 volts (sec), and the relative humidity was 15%.
It has been observed that as the density of these foams increase, the
surface resistivity decreases. All of these foams meet the electrical
specifications of MIL B-81705B for packaging materials for electrostatic
devices and explosives.
Formula 12
(E)
A series of graft foams were prepared as follows, with amounts given as
parts per hundred polyol (php).
______________________________________
MATERIAL 1 2 3 4 5 6
______________________________________
Pluracol 994
50 50 50 50 90 90
Niax 16-56
50 50 50 50 10 10
L6202 1.0 1.0 0.9 0.9 0.7 0.7
Water 5.0 5.0 4.5 4.5 2.75 2.75
Dabco 33LV
0.7 1.1 0.8 1.2 0.7 1.1
Fomrez 0.6 1.0 0.8 1.2 0.7 1.1
UL29
16% Picric
3.0 6.0 3.0 6.0 3.0 6.0
Acid in PCF
TDI (80/20)
57.8 57.8 55.1 55.1 35.8 35.8
DENSITY 1.16 1.25 1.40 1.41 2.10 2.20
(PCF)
SURFACE 1.6E11 8.4E10 3.1E11
1.8E11
9.7E10
3.5E10
RESISTI-
VITY
STATIC 1.2 0.6 1.3 0.8 0.8 0.3
DECAY
______________________________________
Pluracol 994 is a graft polyol of 40% acrylonitrile styrene copolymer
grafted on an ethoxylated propoxylated glycerine (MW 5600), manufactured
by BASF. The surface resistivity is measured as ohm/square. The static
decay is measured at 5000-50 volts (sec), and the relative humidity was
15%.
These picric acid graft foams exhibit excellent antistatic properties.
Formula 12
(F)
A series of picric acid foams were prepared according to the following
basic formulation, with varying amounts of picric acid.
______________________________________
Pluracol 637 100
L6202 1.0
Water 4.6
Dabco 33LV 0.2-1.4
Fomrez UL29 0.3-1.5
16.7% picric acid in PCF
0.1-12
TDI 80/20 49.8
______________________________________
Pluracol 637 is a 20% acrylonitrile styrene copolymer grafted to an
ethoxylated propoxylated glycerin polyol (MW 4200), manufactured by BASF.
These foams exhibited the following resistivities:
TABLE X
______________________________________
VOLUME RESISTIVITY
FOAM PICRIC ACID (php)
(OHM CM)
______________________________________
1 0.017 5.0 E 12
2 0.034 1.9 E 12
3 0.05 5.9 E 11
4 0.10 2.0 E 11
5 0.20 1.1 E 11
6 0.30 6.4 E 10
7 0.40 4.4 E 10
8 0.50 2.5 E 10
9 1.0 1.7 E 10
10 1.5 1.4 E 10
11 2.0 1.1 E 10
______________________________________
This example illustrates the excellent antistatic properties that can be
obtained in picric acid foams at low concentrations. As shown in FIG. 4,
as the concentration of picric acid in the foam rises, the decrease in
resistivity decreases.
Formula 12
(G)
Fire retardant antistatic foam were prepared using picric acid using the
following formulations:
______________________________________
Parts
Material 1 2
______________________________________
Poly G 32-52 100 100
L-5750 1.0 1.0
Water 4.7 4.7
Dabco 33LV 0.8 0.8
Fomrez UL29 0.8 0.8
Methylene Chloride 5.0 5.0
16.7% picric acid in Fyrol PCF
3.0 3.0
Thermolin 101 15.0 0
Antiblaze 100 0 15.0
TDI 80/20 61.0 59.4
DENSITY (PCF) 1.25 1.25
AIR FLOW (CFM) 1.4 1.0
ASTM D-1692 S.E. S.E.
SURFACE RESISTIVITY (ohms/sq.)
4.7 E 10 4.4 E 10
______________________________________
L5750 is a silicone surfactant manufactured by Union Carbide Corp.
Thermolin 101 is Tetrakis (2chloroethyl) diphosphate, manufactured by
Olin. Antiblaze 100 is a chloroalkyl diphosphate ester, made by Mobil
Chemical Co.
This example shows the excellent antistatic properties of flame retardant
foams containing picric acid.
Formula 12
(H)
A prepolymer was made using the following formulations:
______________________________________
Material Parts
______________________________________
Pluracol 994
50
Poly G 32-52
50
TDI 80/20
30
______________________________________
This prepolymer had a Brookfield viscosity of 8000 cps. It was used to
prepare a picric acid antistatic foam using the following formulation.
______________________________________
Material Parts
______________________________________
Prepolymer 130
L6202 1.0
Water 4.6
Dabco 33LV 1.0
Fomrez UL29 0.5
16.7% picric acid in Fyrol PCF
3.0
TDI 80/20 20.8
______________________________________
______________________________________
SURFACE RESISTIVITY (ohms/square)
2.5 E 11
VOLUME RESISTIVITY (ohms cm)
6.8 E 10
______________________________________
These foams have good antistatic properties and can be prepared using a
prepolymer technique, as well as a "one shot" method.
EXAMPLE 13
Hot Water Extraction
Foam 7 from Formula 12 (F) (TABLE X) was washed for 5 minutes in
140.degree. F. water. While washing, the foam was compressed and relaxed
under the hot water to insure maximum water extraction of the antistatic
agent. The foam was then dried for 3 hours at 158 .degree. F. and
conditioned for 16 hours at 75.degree. F. and 50% relative humidity before
measurement of its resistivity. The results are shown in Table XI.
TABLE XI
______________________________________
CONDITIONS VOLUME RESISTIITY (OHMS CM)
______________________________________
No treatment 4.4 E 10
1 Hot water wash
1.4 E 11
2nd Hot water wash
2.4 E 11
______________________________________
These data indicate that picric acid is only slowly extracted from the foam
by hot water.
EXAMPLE 14
Cold Water Extraction
A sample of foam 9 from Formula 12 (F) (Table X) was submerged in water and
placed in a 160.degree. F. oven. This foam was removed weekly, dried,
conditioned and its resistivity was measure. The water was changed weekly.
Following are the results of this test.
TABLE XII
______________________________________
CONDITIONS VOLUME RESISTIVITY (OHMS CM)
______________________________________
Unaged 1.7 E 10
1 week 2.1 E 10
2 weeks 6.1 E 10
3 weeks 9.1 E 10
4 weeks 1.7 E 11
______________________________________
These data indicate that the picric acid was slowly extracted from the foam
by water.
EXAMPLE 15
Graft Foams
Graft antistatic foams were prepared using the following formulations:
______________________________________
Parts
Material 1 2
______________________________________
Pluracol 637 100 100
L6202 1.0 1.0
Water 4.4 4.4
Dabco 33LV 1.0 1.0
Fomrez UL29 1.4 1.2
16.7% picric acid in Fyrol PCF
6.0 0
25% picric acid in Thermolin 101
0 4.0
Forest green 2.0 2.0
TDI 80/20 51.8 49.8
DENSITY (PCF) 1.42 1.45
AIR FLOW (CFM) 1.10 1.50
VOLUME RESISTIVITY (ohms/sq.)
7.2 E 10 3.9 E 10
______________________________________
Forest green is a pigment dispersion No. 4474, manufactured by Pigment
Dispersions Inc., Edison, N.J.
These foams were reticulated and their resistivity was measured:
______________________________________
VOLUME RESISTIVITY (ohm cm)
5.0 E 10 4.3 E 10
______________________________________
These data indicate that there is no loss in conductive properties caused
by the thermal reticulation process.
EXAMPLE 16
Endurance Tests
The reticulated foams of the previous Example were exposed to the following
treatments and their resistivity was measured:
______________________________________
1 2
______________________________________
1. 5 min extraction in methylene
2.7 E 11 2.7 E 11
chloride
2. Dry heat aging 3 hrs 300.degree. F.
5.5 E 10 5.0 E 10
3. Water extraction at 158.degree. F.
1 week 6.1 E 11 4.5 E 11
2 weeks 1.3 E 12 8.4 E 11
3 weeks 4.5 E 12 3.0 E 12
______________________________________
These data indicate that picric acid is slowly extracted by water,
extracted by methylene chloride and essentially unaffected by dry heat
aging.
EXAMPLE 17
Comparative Example
A flexible antistatic foam was made using the following ingredients:
______________________________________
Material Parts
______________________________________
Pluracol 994LV 50
Niax 16 - 56 50
Larostat 377 DPG 5.0
Thermolin 101 5.0
B8028 1.0
Water 3.4
Niax A-10 0.3
Dimethyl benzyl amine
0.8
T-12 0.1
Methylene chloride 4.0
TDI 80/20 44.5
______________________________________
Larostat 377 DPG is an alkyl dimethyl ammonium ethosulfate dissolved in
dipropylene glycol, manufactured by Jordon Chemical Co., Folcroft, PA.
B8028 is a silicone surfactant, manufactured by Goldschmidt Chemical
Corp., Hopewell, VA. Niax A10 is an amine glycol mixture, manufactured by
Union Carbide Corp. T12 is dibutyl tin dilaurate, manufactured by M & T
Chemicals Inc.
This foam had a surface resistivity of 1.8 E 11 ohms/square. The foam was
reticulated. After reticulation, this foam had a surface resistivity of
3.5 E 11 ohms/square.
The reticulated foam containing the quaternary amine antistatic agent was
extracted with water and methylene chloride with the following results:
______________________________________
SURFACE RESISTIVITY
(ohms/sq.)
______________________________________
5 min methylene chloride
1.1 E 12
5 min cold water 7.9 E 11
______________________________________
These data indicate that the quaternary amine is rapidly extracted with
water and methylene chloride.
EXAMPLE 18
Additional Analogs
Various picric acid analogs were evaluated as antistatic charge transfer
agents, as shown below:
TABLE XIII
______________________________________
1. 1 part 4-nitroanisole in 5 parts Fyrol CEF
2. 1 part 4-aminoacetophenone in 5 parts Fyrol CEF
3. 1 part 4-nitrobenzyl alcohol in 5 parts Fyrol CEF
4. 1 part 2-nitroaniline in 5 parts Fyrol CEF
5. 1 part 2,4-dihydroxyacetophenone in 5 parts Fyrol CEF
6. 1 part 4-nitrocatechol in 5 parts Fyrol PCF
7. 1 part 4-nitro-1-naphthol in 43.7 parts TDI
8. 1 part 4-nitrobenzophenone in 43.7 parts TDI
9. 1 part 4-nitrobenzaldehyde in 43.7 parts TDI
10. 1 part 5-nitroanthranilonitrile in 5 parts dimethyl
formamide (DMF)
11. 1 part 2,6-dinitrocresol in 5 parts Fyrol CF
12. 1 part 4-nitroaniline in 5 parts DMF
13. 1 part 2,4-dinitroaniline in 5 parts DMF
14. 2-nitroanisole-liquid used directly
15. 1 part 4-nitrobenzonitrile in 5 parts DMF and 10 parts CEF
16. 1 part 4-nitroacetanilide in 5 parts DMF
17. 1 part 2,4-dinitro-1-napthol sodium salt dilydrate (Martius
yellow) in 7.5 parts DMF
______________________________________
These preparations were incorporated in foams using 1 php of the analog to
be evaluated.
The following foam formulation was used:
______________________________________
Material Parts
______________________________________
32-52 100
L6202 1.0
Water 3.4
Evaluated Compound 1.0
Dabco 33LV 0.5-1.0
UL29 1.0
TDI 43.7
______________________________________
These foams had the properties shown in Table XIV.
TABLE XIV
__________________________________________________________________________
Temp.
Rise
Air Surface
(F.)
Time
Flow
Density
Resistivity
% Relative
Additive (sec)
(cfm)
(pct)
(ohms/sq)
Humidity
__________________________________________________________________________
1. 4-nitroanisol
26 0.3 1.7 6.1 E 11
74/45
2. 4-aminoacetopheone
28 0.26
1.7 9.2 E 11
74/45
3. 4-nitrobenzyl alcohol
27 0.4 1.7 6.7 E 11
74/45
4. 2-nitroaniline
25 0.5 1.7 3.9 E 11
74/45
5. 2,4-dihdroxyacetophenone
27 0.25
1.7 4.4 E 11
74/45
6. 4-nitrocatechol
54 0.4 1.9 8.0 E 10
74/45
7. 2-nitro-1-naphthol
27 0.21
1.6 1.0 E 12
74/45
8. 4-nitrobenzophenone
29 0.14
1.8 1.9 E 12
74/45
9. 4-nitroenzaldehyde
30 0.09
1.6 1.0 E 12
74/45
10. 5-nitroanthranilonitrile
2.3 1.7 4.9 E 11
74/40
11. 2,6-dinitrocresol
119
3.3 1.9 1.4 E 11
74/40
12. 4-nitroaniline
42 6.3 1.7 6.4 E 11
74/40
13. 2,4-dinitroaniline
38 3.8 1.6 3.6 E 11
74/40
14. 2-nitroanisole
54 0.35
1.7 1.4 E 12
74/40
15. 4-nitrobenzonitrile
50 1.21
2.1 1.5 E 11
72/43
16. 4-nitroacetanilide
41 1.45
1.9 4.3 E 11
72/43
17. 2,4-dinitro-1-naphthol
36 2.35
1.8 2.3 E 10
72/43
sodium salt dihydrate
(Martius Yellow)
__________________________________________________________________________
Of these seventeen compounds, all but four easily reduced the surface
resistivity below 1 E 12, but none of the compounds evaluated were as
effective as picric acid (2.9 E 10), which has an effective range of about
0.015 (0.02) to 2.5 php in urethane form.
EXAMPLE 19
Both 4-nitrophenol and 2,4-dinitrophenol exhibit antistatic properties in
urethane foam. Foams were prepared using the following formulation:
______________________________________
Material Parts
______________________________________
32 - 52 100
L 6202 1.0
Water 3.4
4-nitrophenol or 0.5, 1.0, 2.0
2,4 dinitrophenol
Dabco 33LV 0.3, 1.0, 1.2
UL29 0.2, 1.0, 1.5
TDI 80/20 43.7
______________________________________
The surface resistivity of these foams was:
______________________________________
Surface Resistivity (ohms/square)
0.5 php 1.0 php 2.0 php
______________________________________
2,4 dinitrophenol
2.0 E 11 4.3 E 10 1.3 E 10
4-nitrophenol
2.0 E 11 1.0 E 11 5.2 E 10
Picric Acid-control
5.6 E 10 2.9 E 10
______________________________________
These compounds show antistatic properties in urethane foam, which
increases as their concentration increases.
EXAMPLE 20
Rebonded Foam
An antistatic rebonded foam having applications as a package foam for
sensitive electronic equipment was prepared, with picric acid as an
antistatic agent.
A prepolymer was prepared using the following materials:
______________________________________
Material Parts
______________________________________
Poly G 32-52 337
TDI 120
______________________________________
Thirty grams of shredded foam were sprayed with 42 grams of the following
mixture:
______________________________________
Material Parts
______________________________________
Prepolymer 6
16.7 picric acid in Fyrol PCF
6
Methylene Chloride 30
______________________________________
The prepolymer antistatic coated foam was then sprayed with water while the
foam was mixing.
The foam was compressed and cured 5 minutes at 210.degree. F., 30 minutes
at 160.degree. F. and taken out of the mold. The rebonded foam article was
then given a final 5 minute cure at 210.degree. F.
This rebonded foam had the following properties.
______________________________________
DENSITY (PCF) 3.1
SURFACE RESISTIVITY (ohms/sq.)
1.3 E 10
______________________________________
This example illustrates the excellent antistatic properties of a rebonded
foam containing picric acid.
It has been found that foaming with in situ TCNE, picric acid and analogs
thereof produces adequate antistatic properties in conventional foams with
as little as about 0.02 php of the charge transfer agent. Foams made with
graft polyols preferably have approximately at least 0.1 php to achieve
acceptable electrical conductivity when TCNE is the charge transfer agent.
With graft polyol foams containing up to 2.5 php of charge transfer agent
(e.g., TCNE), the electrical resistivity of the finished foam decreases as
the level of agent is increased, but the rate of decrease declines as the
level increases. As with other polyurethane foam products, the amount of
TDI employed in the foam forming reaction depends on the hydroxyl number
of the polyol and the amount of water in the formulation.
Although thermal reticulation of the foam products is preferred (due to
cost and speed consideration) the other reticulation techniques that are
well known in the art including, for example, immersion of the foam in
dilute alkaline solution and exposure to high pressure water and ultra
sound may also be used to reticulate conductive foams made with the charge
transfer agents, according to the invention.
The electrically conductive foam materials of the present invention may be
employed in a variety of military, industrial and consumer applications.
When shaped in the appropriate configuration and sized to the proper
dimension charge transfer agent containing polyurethane foam products can
be used for example as packaging material for voltage sensitive computer
parts to protect them against static electric discharges (e.g. Large Scale
Integrated Circuits), in medical applications (e.g. as grounding mats for
operating room equipment) or as an antistatic carpet underlayer. A
particularly preferred application for the three-dimensional reticulated
charge transfer agent containing foam materials of the present invention
is as a filler material in vehicular fuel tanks and especially those
installed in military aircraft or racing cars.
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